The role of complement in endotoxin-induced disseminated intravascular coagulation: studies in congenitally C6-deficient rabbits

Platelet accumulation induced by bacterial endotoxin in rats

We studied the effects of i.v. administration of endotoxin (Escherichia coli, Serotype 0127:B8) on the kinetics of 111In-labelled platelets within the pulmonary, abdominal and splenic vascular beds of the rat, and on the radioactivity present in dissected samples of splenic and hepatic tissues. Bolus i.v. injection of endotoxin to anaesthetised rats caused a dose-dependent, transient accumulation of 111In-labelled platelets in the pulmonary vasculature. Increased radioactivity, suggestive of platelet sequestration, was detected in tissue samples from both the spleen and the liver at 4.5 h compared to the radioactivity detected in those organs in vehicle treated rats. The modulation of endotoxin-induced platelet accumulation within the lungs, spleen and liver by pharmacological agents was investigated. The pulmonary, hepatic and splenic platelet accumulation induced by endotoxin was unaffected by pre-treatment of the animals with indomethacin, Hirulog or L-NAME. Pre-treatment with dexamethasone significantly reduced the platelet accumulation within the liver and spleen, but not the lungs.

Lipopolysaccharide-induced pulmonary vascular sequestration of polymorphonuclear leukocytes is complement independent

Lipopolysaccharide (LPS) injected intravenously produces leukopenia and sequestration of polymorphonuclear leukocytes (PMN) in the pulmonary vascular bed. To evaluate the role of complement in this process, we used C5-sufficient (B10.D2/nSn) and C5-deficient (B10.D2/oSn) mice and Sprague-Dawley rats depleted of complement with Naja naja cobra venom factor (CVF). We found a comparable increase in the number of PMN in lung tissue of C5-sufficient and C5-deficient mice given Escherichia coli LPS (0127:B8, 3 mg/kg), revealing that LPS acts independently of C5 and its biologically active fragments. Intravenous injection of LPS (3 mg/kg) into rats caused significant intravascular complement activation as assessed by serum CH50 and resulted in an almost 10-fold increase in numbers of PMN in lung tissue. Pretreatment of rats with CVF (50 U) did not reduce LPS-induced PMN sequestration, suggesting that the process is independent of C3. As reported previously, we found large numbers of PMN in bronchoalveolar lavage samples of 24 h after injection of LPS (3 mg/kg). Complement depletion did not prevent LPS-induced migration of PMN. No PMN migration occurred 2, 6, 12, 24, or 48 h after injection of CVF alone, indicating that complement activation is not sufficient to cause PMN migration. In contrast to our findings in rats, no PMN migrated into airspaces of C5-sufficient and C5-deficient mice 24 or 48 h after injection of LPS (3 to 20 mg/kg).

The pulmonary vascular sequestration of neutrophils in endotoxemia is initiated by an effect of endotoxin on the neutrophil in the rabbit

Endotoxemia causes neutrophil sequestration in the pulmonary vascular bed. Such sequestration may be a critical initiating event in the generation of microvascular injury, although the mechanisms that lead to this localization are not understood. To investigate these phenomena, the following study employed intravenous pulses of 111Indium-tropolonate-labeled neutrophils (111In-neutrophils), which circulated in the rabbit with normal kinetics and responded in a manner indistinguishable from unlabeled, circulating neutrophils in response to an intravenous injection of purified endotoxic lipopolysaccharide (LPS) or epinephrine. Pulmonary sequestration of 111In-neutrophils was assessed by quantitative external gamma camera scintigraphy of a lung suprahilar region of interest. Noninvasive assessment of radioactivity by this method accurately reflected total lung radioactivity, which was shown by autoradiography to be confined to the injected 111In-neutrophils. Intravenously administered LPS caused a marked, dose-dependent sequestration of 111In-neutrophils in the pulmonary vasculature, and exhaustive ultrastructural autoradiography showed discretely radiolabeled neutrophils located within pulmonary capillaries. A distinct effect was seen with an intravenous injection of as little as 100 ng per rabbit (i.e., 500 pg/ml blood). A 5-min ex vivo pretreatment of 111In-neutrophils with 10 ng to 10 micrograms/ml LPS in heat-inactivated plasma (which resulted in retention of as little as 500 pg LPS per 10(7) neutrophils) also caused dose-dependent pulmonary sequestration of the pretreated 111In-neutrophils but did not cause generalized neutropenia in recipient rabbits. There was no evidence of complement activation on the surface of pretreated neutrophils.(ABSTRACT TRUNCATED AT 250 WORDS)

Neutrophil-mediated pulmonary vascular injury. Synergistic effect of trace amounts of lipopolysaccharide and neutrophil stimuli on vascular permeability and neutrophil sequestration in the lung

The pathogenesis of acute lung injury in humans is obscure, but lipopolysaccharide (LPS), complement activation, and neutrophils have been implicated. We investigated in rabbits the interaction of small amounts of intravascularly administered LPS (100 ng) with neutrophil chemotactic factors, the synthetic chemotactic peptide formyl-norleucyl-leucyl-phenylalanine (FNLP), and the biologically relevant chemotactic fragments of C5 (C5f). These neutrophil stimuli produce neutropenia when injected intravascularly in rabbits, reflecting neutrophil adherence to vascular endothelium. When LPS was injected with FNLP, the duration of neutropenia was enhanced. Studies with radiolabeled neutrophils infused in vivo demonstrated prolonged neutrophil sequestration within the lung in rabbits that were given FNLP plus LPS, an effect that was visible for 4 h after injection. Morphometric analysis of tissue sections 4 h after infusion confirmed the presence of greater numbers of neutrophils in the lungs of animals receiving LPS and FNLP. When a combination of LPS and chemotactic factors was infused at both zero and 6 h, we found a marked enhancement of lung vascular permeability at 24 h (as assessed by radiolabeled albumin accumulation), an effect not seen with either LPS or chemotactic factor alone. Ultrastructural studies revealed neutrophil sequestration and alteration in endothelial cells in the animals that received the combination of LPS and chemotactic factors. Neutrophil depletion with nitrogen mustard completely abolished the increased vascular permeability seen in animals that received LPS and chemotactic factors. This study suggests that small amounts of intravascularly administered LPS enhance the sequestration of neutrophils within the lung and increase lung vascular permeability and endothelial injury caused by neutrophils stimulated by intravascularly administered chemotactic factors. This mechanism may be relevant to the production of acute lung injury in human beings.

Platelet activating factor (PAF) involvement in endotoxin-induced thrombocytopenia in rabbits: studies with FR-900452, a specific inhibitor of PAF

PAF (1 ug/kg) injected intravenously (i.v.) into anesthetized rabbits resulted in marked loss of circulating platelets and leukocytes. Administration of FR-900452 1-methyl-3-(1-(5-methylthiomethyl-6-oxo-3-(2-oxo-3-cyclopenten-1-y lidene)- 2-piperazinyl) ethyl)-2-indolinone, a specific PAF inhibitor, at a dose of 10 mg/kg i.v. with 10 min prior to the PAF injection significantly prevented both changes. On the other hand, PAF has been considered as a mediator of endotoxin shock. Therefore, in order to determine whether endogenous PAF contributes to the occurrence of thrombocytopenia or leukopenia in endotoxin shock, we assessed the effect of FR-900452 on the thrombocytopenia and the leukopenia following bolus i.v. injection of E.coli endotoxin (0.03 mg/kg) in rabbits. As a result, pretreatment with the compound (10 mg/kg, i.v.) significantly reduced the thrombocytopenia at 60 and 180 min after the endotoxin injection. In contrast, FR-900452 did not reduced the leukopenia at any time of after endotoxin. These results indicate that PAF might be involved in the occurrence of thrombocytopenia in rabbit endotoxemia and the contribution of PAF to the leukopenia is much less extent than that to the thrombocytopenia.

Endotoxin in meningococcal infections

26 children with meningococcal infections were studied to find out the relationaship between plasma and cerebrospinal fluid levels of endotoxin, the clinical outcome, the level of antigen in plasma and cerebrospinal fluid, and indices of complement activation and disseminated intravascular coagulation. No association was found between endotoxin levels and the other factors. A high cerebrospinal fluid antigen level in patients with meningitis was associated with a poor prognosis.

Role of complement in endotoxin initiated lethality in mice

We have examined the role of complement in eliciting a lethal response in C3H/HeJ and C3H/St mice. The results reported here indicate that endotoxin-initiated complement activation, leading to significant drops in circulating C3 levels, is not sufficient to cause lethality. The complement system in both strains was demonstrated to be responsive in vitro to activation both by E. coli 0111:B4 LPS I, an alternative pathway activator in other systems, as well as S. minnesota R595 LPS, which activates almost exclusively the classical pathway. In vivo injection of high (lethal) doses of E. coli 0111:B4 LPS I and S. minnesota R595 LPS causes a significant decrease in the circulating C3 levels of both strains after 4 hr. In contrast, circulating C3 levels were not significantly different from normal values in either strain following injection with minimal (lethal) amounts of E. coli 0111:B4 LPS II, a weakly anticomplementary LPS preparation. In all cases, lethality was observed in only the C3H/St mice, indicating that neither complement activation, nor the lack of it, is responsible for lethality in mice.

Unilateral Shwartzman reaction: cortical necrosis in one kidney following in vivo perfusion with endotoxin

Unilateral renal cortical necrosis was selectively induced by in situ perfusion of the rabbit kidney with a perfusate containing 50 microgram of endotoxin followed by the i.v. administration of 250 microgram of endotoxin 24 hr later. The results strongly support the idea that the initial event in the genesis of renal cortical necrosis during the Shwartzman reaction is a specific local effect of endotoxin on the vascular endothelium.

[Relations between complement and blood coagulation (author's transl)]

The complement system as well as the blood coagulation system are involved in several disease processes so that it seems to be of interest to search for direct or indirect functional relations. Both systems can be activated in vitro as well as in vivo by the same substances, as e.g. endotoxin or antigen antibody complexes. In spite of these common characteristics a direct functional relationship between complement and plasmatic blood coagulation could not be established. Complement and blood coagulation do not interact with each other. Activated complement components, however, can induce platelet aggregation and release reaction both of which may accelerate but not trigger intravascular coagulation. Therefore, indirect relations between complement and blood coagulation can be found in patients or in animal experiments, especially after activation of intravascular coagulation. These interactions depend on further mediator sugstances of both systems.

Mediation systems in bacterial lipopolysaccharide-induced hypotension and disseminated intravascular coagulation. I. The role of complement

We have studied the role of complement in lipopolysaccharide (LPS)-induced hypotension and disseminated intravascular coagulation (DIC) by comparing the effects of injection of three preparations of LPS from E. Coli 0111:B4, S. minnesota Re595, and S. marcescens. Injections of nonlethal doses of these LPS preparations into normal rabbits produced decreases in mean arterial blood pressure during a 5-h period. When rabbits treated with cobra venom factor (CoF) to deplete C3 were injected with the various LPS preparations, mean arterial pressures fell at a rate and extent essentially identical to that observed in normal rabbits. Rabbits genetically deficient in C6 also demonstrated LPS-induced hypotensive changes. Only minimal, or no changes in plasma C3 levels or serum CH50 values were detected in normal rabbits after LPS injection. Hypotensive changes were also induced in rabbits when complement was rapidly activated by intravenous injection of CoF. In contrast to the hypotension induced by LPS, the fall in arterial pressure associated with the consumption of complement was short lived and required the rapid consumption of considerable amounts of C3. The occurrence of DIC noted in normal rabbits injected with each preparation of LPS was not inhibited in either rabbits treated with cobra factor or in C6-deficient rabbits. The DIC was most pronounced after injection of Re595 and S. marcescens LPS. Injection of the various LPS preparations produced a rapid disappearance of circulating neutrophils and mononuclear cells, which occurred with the same kinetics and to the same extent in normal, CoF-treated, and C6-deficient rabbits. Injection of either Re595 LPS or S. marcescens LPS produced a biphasic disappearance of circulating 51Cr-platelets. In contrast, injection of 0111:B4 LPS affected only slightly the rate of disappearance of 51Cr-platelets. Depletion of C3 by cobra factor treatment had no effect on the disappearance of platelets in animals injected with 0111:B4. In marked contrast cobra factor treatment greatly reduced the initial rapid disappearance of platelets in rabbits injected with either Re595 or S. marcescens LPS, but had no effect in the secondary disappearance phase.